NEW YORK — The New York City medical examiner’s office confirmed Friday that it is reviewing hundreds of rape cases for possible errors in DNA analysis.

Officials say so far it appears that the testing in the majority of the cases was valid. But in one instance, the review uncovered evidence that resulted in an indictment last year accusing a man of raping a minor more than a decade ago in Brooklyn.

The exhaustive review, first reported in The New York Times, began after the medical examiner’s office found errors by an unidentified lab technician, who was hired in 2001 and quit in 2011, spokeswoman Ellen Borakove said.

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During a training session before her resignation, supervisors learned that her ‘‘work wasn’t up to the standards we expect,’’ Borakove said.

The medical examiner’s office determined that the technician had handled evidence in more than 800 sexual assault cases during her nine-year tenure. The review, which is more than half completed, has found she failed to find existing biological evidence in at least two dozen instances.

Authorities stressed Friday that while the review could result in new charges in old cases, there was no indication the faulty work resulted in convictions of innocent people.

In some instances, the technician reported she found no potential DNA evidence on clothing, according to the review. Re-tests by others found stains that tested positive for blood and semen.